This invention relates to hydraulically powered rotary percussive machines of the kind which are used as rock drilling machines.
Hydraulic percussive drilling machines are known in which a piston is caused to reciprocate to and fro and a rotation motor is arranged to rotate a chuck holding the tool upon which the piston is caused to impact--see U.S. Pat. Nos. 4,006,783 and 4,430,926.
In U.S. Pat. No. 4,006,783 the percussion motor and the rotation motor are on separate hydraulic circuits. This necessitates the use of four hydraulic hoses between the hydraulic power pack and the machine. In U.S. Pat. No. 4,430,926 the percussion motor and the rotation motor are on a common feed with only two hoses between the power pack and the machine. In the latter case the feed passes through at least one valve of the constant volume flow dividing type which establishes priority of flow to the rotation motor and bypass flow to the percussion motor after a predetermined constant flow to the rotation motor has been established. These constant volume flow dividing priority valves are expensive and difficult to fit in the space normally available in a rock drill casing.